1. Field of the Invention
The present invention relates to a package for a semiconductor integrated circuit, for example, which operates in a high-frequency band of several tens MHz or over.
2. Description of the Prior Art
FIG. 4A is a plan view showing a conventional metal base type package while FIG. 4B is a sectional view taken along the line C--C of FIG. 4A.
Referring to FIGS. 4A and 4B, in a microwave IC package 30, space 2 for mounting IC chip (referred to as "cavity" hereinafter) is provided in a metal base 1 while a metal ring 3 for shielding is fixed through a mount 3a of insulating material to the metal base 1, surrounding the cavity 2.
On the right and left sides of the cavity 2, microstrip-shaped feedthroughs 4a, 4b are formed. The feedthroughs 4a, 4b are formed by patterning a conductor, such as gold and the like, to form microstrip lines on dielectrics of ceramic or the like, and they extend from opposite ends of the metal base 1 under the mount 3a until they reach the cavity 2.
The feedthrough 4a is used as an RF terminal for input while the feedthrough 4b is used as an RF terminal for output.
Similarly, on a dielectric 6 of ceramic or the like DC terminals 8a, 8b, 8c are formed by patterning a conductive material, such as gold and the like, in the direction orthogonal to the shaft line of the feedthroughs 4a, 4b.
A single or a plurality of high-frequency IC chips are attached to the cavity 2; FIG. 5 shows an example when two high-frequency IC chips are mounted. In this example, high-frequency IC chips 5a, 5b are fixed on the cavity 2 by means of soldering, using adhesive agent or the like, and connected with each other by wire 9 while each of them is connected to the feedthroughs 4a, 4b and the DC terminals 8a, 8b, 8c in the similar way. For those connections, ribbon bond or the like may be employed instead of the wire bond.
In a configuration of the above-mentioned microwave IC package, since the feedthrough 4a for input and the feedthrough 4b for output are opposite to each other and close to each other with the cavity 2 interposed therebetween, part of an input signal from the feedthrough 4a for input may leak immediately to the feedthrough 4b for output without passing to the high-frequency IC chips 5a, 5b; hence, there is the disadvantage that isolation between the input and output of the package 30 deteriorates and an excellent switching device cannot be obtained.